一．用SqlConnection连接SQL Server

1..加入命名空间

using System.Data.SqlClient;

2.连接数据库

SqlConnection myConnection = new SqlConnection();

myConnection.ConnectionString = "user id=sa;password=sinofindb;initial catalog=test;data source=127.0.0.1;Connect Timeout=30";

myConnection.Open();

改进（更通用）的方法：

string MySqlConnection="user id=sa;password=sinofindb;Database =test;data source=127.0.0.1;Connect Timeout=30";

SqlConnection myConnection = new SqlConnection(MySqlConnection);

myConnection.Open();

二、用OleDbConnection连接

1.加入命名空间

using System.Data.OleDb;

2.连接sql server

string MySqlConnection="Provider=SQLOLEDB;Data Source=localhost;Initial Catalog=test;Integrated Security=SSPI;";

SqlConnection myConnection = new SqlConnection(MySqlConnection);

myConnection.Open();

3.连接Access(可通过建立.udl文件获得字符串)

string MySqlConnection="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\db2000.mdb;

Persist Security Info=False;

4.连接Oracle(也可通过OracleConnection连接)

string MySqlConnection="Provider=MSDAORA;Data Source=db; user id=sa;password=sinofindb";

三.创建Command对象

1．SqlCommand 构造函数

①初始化 SqlCommand 类的新实例。public SqlCommand();

SqlCommand myCommand = new SqlCommand();

②初始化具有查询文本的 SqlCommand 类的新实例。public SqlCommand(string);

String mySelectQuery = "SELECT * FROM mindata";

SqlCommand myCommand = new SqlCommand(mySelectQuery);

③初始化具有查询文本和 SqlConnection 的SqlCommand类实例。

Public SqlCommand(string, SqlConnection);

String mySelectQuery = "SELECT * FROM mindata";

string myConnectString = "user id=sa;password=;database=test;server=mySQLServer";

SqlConnection myConnection = new SqlConnection(myConnectString);

SqlCommand myCommand = new SqlCommand(mySelectQuery,myConnection);

④初始化具有查询文本、SqlConnection 和 Transaction 的 SqlCommand 类实例。

public SqlCommand(string, SqlConnection, SqlTransaction);

SqlTransaction myTrans = myConnection.BeginTransaction();

String mySelectQuery = "SELECT * FROM mindata";

string myConnectString = "user id=sa;password=;database=test;server=mySQLServer";

SqlConnection myConnection = new SqlConnection(myConnectString);

SqlCommand myCommand = new SqlCommand(mySelectQuery,myConnection, myTrans);

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连接SQL
例DAL层下的Database   
private static readonly string strConn = ConfigurationManager.ConnectionStrings["StuConn"].ConnectionString;//
web.config
        <connectionStrings>
                <add name="StuConn" connectionString="Data Source=XP-201103092021; DataBase=chenggong; Uid=sa; Pwd=citsoft" providerName="System.Data.SqlClient"/>
        </connectionStrings>